1. Field of the Invention
The present invention relates to an electrical wire insulation stripping method and stripping device suited to use with electrical wires of wound wire type used for automotive ignition cables.
2. Description of the Prior Art
Conventional ignition cable used in the ignition circuit of an automobile is a wound shielded cable, which as shown in FIG. 6 has a tension member 1 core of an aramid or other polymer fiber covered successively with a silicon rubber and ferrite powder composition insulation layer 2, a layer of wire 3 having a predetermined electric resistance and made of stainless steel or another metal alloy wrapped in a spiral pattern around the insulation layer 2, an insulation layer 4 of an EP rubber or other composition covering the outside of the wound resistance wire 3, a braiding 5 of glass fiber formed around the insulation layer 4, and a sheath 6 of silicon rubber wrapped around the outside of the braiding 5. Cables of this type have been described in Japanese Utility Model Publication (examined) H1-32253.
A flexible wrapped core 7 is formed by the tension member 1 and the silicon insulation layer 2, and an outside coating 8 is formed by the insulation layer 4, braiding 5, and the sheath 6 to insulate the resistance wire 3.
The conventional procedure followed to connect this wound electrical wire 10 to a terminal connector is described below with reference to FIGS. 7A to 7D.
As shown in FIG. 7A, a predetermined length L of the wound electrical wire 10 supplied from a coiled drum is first cut (the cutting step).
Next, as shown in FIG. 7B, the end outside coating 8a at the end of the electrical wire 10 is stripped off, forming the stripped resistor 12 in which the resistance wire 3 is exposed (the stripping step). When stripping the end outside coating 8a, the frictional resistance and drag acting between the end outside coating 8a and the resistance wire 3 due to the wrapping of the resistance wire 3 around the flexible core 7 causes the resistance wire 3 wrapped around the flexible core 7 to unravel as the end outside coating 8a moves lengthwise along the electrical wire 10.
Then as shown in FIG. 7C, the resistance wire 3 and flexible core 7 are cut by conductor cutting knives 13 to leave a stripped resistor 12 of a predetermined length D (the conductor cutting step), removing the unravelled part of the resistance wire 3 by removing the excess length of the stripped resistor 12.
Then as shown in FIG. 7D, the stripped resistor 12 is bent to the outside circumference side of the sheath 6 and an electrical connection is made between the resistance wire and the terminal connector 14 by crimping the terminal connector 14 to hold the bent part of the stripped resistor 12 (the connector crimping step), thus completing connection of the terminal connector 14 to the electrical wire 10.
A terminal connector 14 is also connected to the other end of the wound electrical wire 10 in the same way.
However, when the outside coating 8 is stripped from the electrical wire 10 to connect the terminal connector 14 as described above, the next step after the stripping step is completed is the conductor cutting step. Because only the electrical wire 10 side of the stripped resistor 12 is supported during the conductor cutting step as shown in FIG. 7C, the softness and flexibility of the flexible core 7 makes the stripped resistor 12 sag in an unstable manner; this makes it difficult to cut the stripped resistor 12 in a straight line, normally resulting in a certain amount of sag or bending. Depending upon the degree and direction of this sag or bending, the conductor cutting knives 13 contact the stripped resistor 12 when lowered to the cutting position in the conductor cutting step, increasing the bend in the stripped resistor 12 and causing the stripped resistor 12 to escape from the cutting position. The cutting operation of the conductor cutting knives 13 in this state does not cut the stripped resistor 12, thus resulting in problems caused by the non-removal of the unravelled part of the resistance wire 3.
If the connector is crimped with the unravelled part of the resistance wire 3 present, the unravelled resistance wire 3 will extend outside the sheath 6 and the terminal connector 14. When the assembled wire and connector is then assembled to the distributor cap for the spark plugs, the unravelled end of the resistance wire 3 may be pulled farther out. This may cause current leakage from the unravelled resistance wire 3 and contribute to engine trouble when the cable is then used as an ignition cable in a motor vehicle.